Lubricating composition having a reduced coking tendency



United States Patent opment Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Filed Oct. 10, 1960, Ser. No. 61,385

3 Claims. (Cl. 25245) This invention relates to an improved lubricating composition and more particularly to an improved hydrogenated mineral lubricating oil suitable for high temperature lubrication.

The current trend in designing more eflicient and more economical automotive and aircraft engines has accentuated the need for lubricants which will effectively lubricate bearings operating under severe conditions, particularly under high temperature conditions. While considerable progress has been made in recent years in producing improved lubricants, some difficulty has been encountered in producing a lubricant which will effectively lubricate bearings opera-ting at high temperatures for prolonged periods of time.

For many years, highly refined parafiinic oils have been used as base oils in forming lubricating compositions. By the term highly refined parafiinic oil we mean a petroleum lubricating oil which has been refined by one of the more drastic refining methods known in the art, for example, by conventional aluminum chloride refining and solvent extraction adapted to remove all or substantially all of the unsaturated and aromatic constituents of the oil. Aluminum chloride refined or solvent extracted paraifinic oils, such as the Pennsylvania oils, have provided excellent base oils for many lubricating compositions. Likewise, drastically refined Mid-Continent and Gulf Coastal oils have been widely used as base oils in forming lubricants. In addition to these refining methods, lubricating oils of high quality have been obtained by hydrogenating various charge stocks derived from Pennsylvania, Mid-Continent, West Coast, Middle- East crudes, etc. It has been known, for example, that improved lubricating properties can be obtained when the lubricating oil stocks are treated with hydrogen. Trea-ting some lubricating oil stocks with hydrogen, for example, h-as resulted in excellent multigrade lubricants, i.e., lubricants suitable for use under a wide range of temperatures. Not all of the hydrogenated oils, however, are sufficiently stable at an elevated temperature to meet the low coking requirement of the United States Air Force for certain aviation lubricants. The tolerable coking tendency of a lubricating oil is set forth in the 700 F. panel coker test in Specification MIL-L- 9236A.

We have discovered that a lubricating composition having reduced coking tendencies can be obtained by incorporating into a hydrogenated mineral oil a small amount of a compound having the following structural formula:

R S/ R R R where R is selected from the group consisting of hydrogen, alkyl, aryl, aralkyl, alkaryl and cycloalkyl radicals each one of which contains not more than 14 carbon atoms. Thus, the improved lubricating composition of our invention comprises a major amount of a hydrogenated 3,095,377. Patented June 25, 1963 ICC mineral oil and a small amount, sufiicient to reduce the coking tendencies of the oil, of a compound of the type designated by the above structural formula.

The R radicals can be like or unlike substituen-ts including hydrogen, methyl, ethyl, propyl, butyl, pentyl, hexyl, hep tyl, octyl, nonyl, decyl, undecyl, dodecyl, tl'i'r decyl, tetradecyl, phenyl, naphthyl, benzyl, tolyl, cyclopentyl and cyclohexyl radicals.

More specifically, compounds within the above formula l-methyl dibenzothiophene Z-me'thyl dibenzo-thiophene 3-methyl dibenzothiophene 4-methyl dibenzothiophene 6-methyl dibenzothiophene 7-methyl dibenZ-othiophene S-methyl dibenzothiophene 9-methyl dibenzothiophene 2,8-dimethyl dibenzothiophene 2,4,6,8-tetramethyl dibenzothiophene 1,2,3,4,6,7,8,9-octamethyl dibenzothiophene 2-ethyl dibenzothiophene l-p'ropyl dibenzothiophene 2-n1butyl dibenzothiophene S-tert-butyl dibenzothiophene 4-pentyl dibenzothiophene 6-hexyl dibenzothiophene 7 -heptyl dibenzothiopheue 8-octyl dibenzothiophene 9-nony1 d-ibenzothiophene 1-decyl dibenzothiophene Z-undecyl dibenzothiophene 3-dodecyl dibenzothiophene 4-tridecyl dibenzothiophene o tetradecyl dibenzothiophene 2-phenyl dibenzothiophene Z-naphthyl dibenzothiophene 2-benzyl dibenzothiophene 2-t-oly1 d-ibenzothiophene Z-cyclopentyl dibenzothio-phene 2-cyclohexyl dibenzothiophene Z-n-butyl-S-tert-butyl dibenzothiophene 2,8-di-tert-butyl-4,6-di-methyl dibenzothiophene The dibenzothiophenes can be prepared according to known chemical procedures. Neither the compounds per se nor their method of preparation constitutes any portion of the invention.

The amount of dibenzothiophene or its derivatives which we employ is an amount sufiicient to reduce the coking tendency of the oil. In most instances, this amount will be in the order of about 0.5 to about 1 percent by weight based on the weight of the hydrogenated oil. In some instances, however, particularly with the derivatives of dibenzothiophene, the amount will be in theorder of about 0.5 to about 5 percent by weight based on the weight of the hydrotreated oil.

Dibenzothiophene or its derivatives can be incorporated in the hydrogenated base oil as such or it can be added to the oil in the form of a concentrated solution. The use of a concentrate is particularly advantageous where the amount of additive employed exceeds its solubility limit in the base oil. Any solvating agent which does not adversely affect the other desirable properties of the lubricant can be used.

The hydrogenated mineral lubricating oil which is employed in producing the composition of the invention can be obtained by any hydrogen treating process wherein extensive hydrogenation of the olefinic and/or aromatic constituents present in the charge stock has been effected. Ring opening may occur as well. Thus, the method by which a hydrogenated mineral lubricating oil is obtained is not a part of the present invention. The charge stock employed in the hydrogen treating process can be derived from any type of crude, such as Pennsylvania, Mid-Continent, West Coast, Middle-East crudes, etc. The charge stock can be either a distillate fraction or a deasphalted residum.

The hydrogen treatment employed in obtaining a suitable hydrogenated mineral lubricating oil can be carried out at a pressure between about 200 and about 10,000 p.s.i.g.; a temperature between about 400 and about 850 F.; at a space velocity between about 0.1 and about 16 volumes of charge stock per volume of catalyst per hour; and at a hydrogen recycle rate between about 100 and about 20,000 standard cubic feet per barrel of charge. One known method of hydrogen treating lubricating oils is a mild type of operation to effect decoloration and hydrogenation of easily hydrogenated materials such as olefins. This procedure gives very little if any improvement in viscosity index and little if any change in viscosity. This mild operation is carried out at a pressure between about 200 and about 2,000 p.s.i.g., at a temperature between about 450 and about 650 'F., at a space velocity between about 0.1 and about 8.0. Any hydrogenation catalyst can be used such as nickel, cobalt, platinum and oxides and sulfides of group VI and group VIII metals such as molybdenum, tungsten, nickel, cobalt, etc. oxides and sulfides or mixtures thereof. Porous supports can be used. Such procedures can be used to prepare a suitable hydrogenated mineral lubricating oil for use in the composition of the present invention.

Another known method of hydrogenating lubricating oils is more severe than the above discussed hydrogen treatment. In this process the objective is not only to bydrogenate materials which are easily hydrogenated such as olefins, but also to effect hydrogenation of aromatics. In this type of process, a moderate improvement in viscosity index and slight reduction in viscosity is obtained, indicating that some hydrocracking has occurred. This process is carried out in the presence of mixtures of a sulfide or a metal of the iron group mixed with a sulfide of a metal of group VI of the periodic system. These catalysts may be unsupported or supported on porous carriers. In the event a supported catalyst is employed, the carrier may be activated alumina, pumice, silica-alumina mixtures, etc. Pressures usually employed are about 500 to about 5,000 p.s.i.g., temperatures between about 650 and about 725 F. at a space velocity between about 0.1 and about 4.0. This type of process may also be used in preparing a hydrogenated mineral lubricating oil for use in the composition of the invention.

A third type of lube oil hydrogen treatment is known in which extensive change takes place in the viscosity index and viscosity of the charge stock. In this type of process the same catalysts can be employed that are mentioned in connection with the second type of hydrogen treatment. Pressures employed are between about 1000 and 10,000 p.s.i.g.; temperatures are between about 725 and 825 F.; and space velocities are usually between about 0.4 and about 1.5. One aspect of the last mentioned type of process is the preparation of multigrade lubricating oils. In the event such a product is desired, the charge stock should have a viscosity index above about 60.

The hydrotreated oils used in illustrating compositions of the invention are multigrade hydrotreated mineral lubricating oils. Such oils can be obtained by blending separate fractions of a hydrotreated deasphalted reduced crude. The following example will illustrate the preparation and properties of multigrade 10W/ 20 and 20W/3O oils.

EXAMPLE 1 An Ordovician reduced crude having the properties given in Table I is charged to a propane deasphalting unit to yield a product with specifications also shown in Table I.

Table l Reduced Propane Inspection Data Crud Deasphalted Gravity, API 16.4 23. 5 Viscosity, SUS at 210 F 480 102 Viscosity Index Carbon Residue (Conradson) Percent 8. G 1. 8 Flash Point, F 615 540 Fire Point, F 705 075 Four Point, F +40 +80 Iodine N0 14.1

The propane deasphalted product is treated with hydrogen at a pressure of 3530 p.s.ig. at a temperature of 764779 F., using a space velocity of 0.5, and a gas recycle rate percent hydrogen) of 5000 s.c.f. per barrel in the presence of a presulfided 25 percent nickeltungsten, 1 percent fluorine on silica-alumina catalyst. The hydrotreated product after a high pressure separation of hydrogen is topped at atmospheric pressure to remove the furnace oil and lighter hydrocarbons (670 F. end point). The bottoms fraction is then topped in a vacuum distillation to remove the light lubricating fraction (670-725 F.). .The remaining product is dewaxed by treating with 4 volumes of a 60-40 methyl ethyl ketonetoluene mixture followed by cooling to 0 F. After removal of the dewaxing solvent, the dewaxed product is fractioned in vacuum distillation to obtain a light blending oil and a heavy blending oil. The heavy blending oil is a 20W/ 30 hydrotreated oil. A 10W/20 oil is made by blending 44 percent of the light blending oil with 56 percent of the 20W/30 oil. To improve the color of the 20W/ 30 oil due to darkening during distillation this stock is hydrofinished at 625 F, 1000 p.s.i.g., 2000 s.c.f. of

0 hydrogen per barrel of charge and a 4.0 liquid hourly space velocity using a nickel cobalt-molybdenum on alumina catalyst. In preparing the compositions shown below, 0.2 percent by weight of 2,6-di-tertiary-butyl-4 methylphenol was added as an anti-oxidant to both the light and heavy blending oils. Typical properties of these oils are as follows:

10VV/20 20'\V/30 Inspection Data Hydro- Hydrotreatctl treated i1 Oil Viscosity SUB:

at 0 is 9. 900 so, 000 220 457 50. 4 00. 0 124 117 0. 01 0. 01 3. 2. 1

EXAMPLE 2 A multigrade 20W/40 hydrogenated oil is obtained by treating the charge stock used in Example 1 under conditions identical to those employed in Example 1 at a temperature of 745 F., a space velocity of 0.5, a pressure of 3000 p.s.i.g. and a hydrogen recycle rate of 5000 s.c.f. per barrel of charge. The same catalyst is employed as in Example 1 and the product is dewaxed and fractionated in a manner similar to that shown in Example 1 to obtain various cuts. A fraction distilling above 890 F. is col- A lected as the multigrade 20W/40 hydrogenated oil. Typical properties of this oil are as follows. r

. 6 Specific examples of other compositions within the scope of the invention are set forth in Table. III.

, Table III Composition, percent by weight 10W/20 Hydrotreated oil W/30 Hydrotreated oil 2OW/40 Hydrotreated oil Dibenzothionhpnp 2-Methy1 dibenzothionhem 2,8-Dimethyl dibenzothiophena- 2,8-Di-tert-butyl-4,6-dl -metl1yl benzothiooh n 2-Tetradecy1 (libenzothiophpene 2-1henyl dibenzothiophene 2-Naphthy1 dibenz0thiophene 2-Benzyl dibenzothiophene 2-Oyc1opentyl dibenzothiophene 2-Oyclohexyl dibenzothionhonp In order to illustrate the reduced coking tendencies of a lubricating composition of the invention, a multigrade 20W/ 30 hydrotreated oil was compared with the same oil containing 1 percent by weight of dibenzothiophene according to a modified panel coker test described in paragraph 4.5.9 of Specification MIL-L-9236A. The apparatus used in this test is described in Detailed Handbook on Test Procedures in Support of Turbojet and Turboprop Lubricants, March 1957, Wright Air Development Center. The modified procedure used in this example differs from that described in the reference only in that (1) only enough oil (which is often available only in small quantity) is placed in the reservoir to keep the sump at the required level during the test period and (2) the edges of the panels are not scraped to remove coke.

The panel deposit weights listed in Table II show clearly the reduced coking tendency of the oil containing dibenzothiophene.

Table 11 Panel coker test, 700 F.,

Oil composition: 8 hr. coke, mg.

20W/ 30 hydrotreated oil 83 20W/ 30 hydrotreated oil plus 1% dibenzothiophene 59 The above data in Table II show that the coking tendency of the hydrotreated oil is reduced by about one third when 1 percent of dibenzothiophene is added to the oil. The reduction in the coking tendency of the hydrogenated oil by the addition of dibenzothiophene is surprising when viewed in the light of the results obtained with an unhydrogenated oil. For example, a solvent extracted mineral lubricating oil gave 90 mg. of coke in the above-described panel coker test. When 1 percent of dibenzothiophene was added to the same unhydrogena-ted oil, 96 mg. of coke were obtained. Thus, the coking tendency of an unhydrogena-ted oil is not reduced by the addition of 1 percent of dibenzothiophene.

The lubricating oil composition of the invention can contain other addition agents normally added to lubricating oils for a specific purpose such as an oiliness and extreme pressure agent, an anti-oxidant, a corrosion inhibitor, a foam suppressant, a dye, a sludge inhibitor, a viscosity index improver, and the like. These agents can be separately added to the oil or they can be added in the form of a solution which contains one or more of such additives. If desired, the solution can also contain the dibenzothiophene compound.

While our invention has been described with reference to various specific examples and embodiments, it will be understood that the invention is not limited to such examples and embodiments and may be variously practiced within the scope of the claims hereinafter made.

We claim:

1. A lubricating composition comprising a major amount of a hydrogenated miner-a1 lubricating oil and a small amount, sufiicient to improve the coking tendencies of the oil, of a compound having the following structural formula:

Where R is selected from the group consisting of hydrogen, alkyl, aryl, aralkyl, alk-aryl and cycloalkyl radicals each one of which contains not more than 14 carbon atoms.

2. A lubricating composition having a reduced coking tendency comprising a major amount of a hydrogenated mineral lubricating oil and about 0.5 to about 5 percent by weight of a compound having the following structural formula:

a \S/ R R R where R is selected from the group consisting of hydrogen, alkyl, aryl, ar-alkyl, alkaryl and cycloalkyl radicals each one of which contains not more than 14 carbon atoms.

3. A lubricating composition having a reduced coking tendency comprising a major amount of a hydrogenated mineral lubricating oil and about 0.5 to about 1 percent by weight of dibenzothiophene.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Shoemaker et a1 May 30, 1939 Richter et a1 Aug. 16, 1949 Reiff et al. Nov. 7, 1950 5 Richter et a1. Nov. 7, 1950 Richter et a1. Oct. 16, 1951 Goodhue et al. Jan. 5, 1954 FOREIGN PATENTS Great Britain May 11, 1937 OTHER REFERENCES Cole et 21.: Survey of the Literature on Antioxidants and Anticorrosion Additives for Lubricants at Elevated Temperatures, WADC Technical Report 53-353, p. 103, May 1954. 

1. A LUBRICATING COMPOSITION COMPRISING A MAJOR AMOUNT OF A HYDROGENATED MINERAL LUBRICATING OIL AND A SMALL AMOUNT, SUFFICIENT TO IMPROVE THE COKING TENDENCIES OF THE OIL, OF A COMPOUND HAVING THE FOLLOWING STRUCTURAL FORMULA: 